If you've been wanting the use your DualShock 4 wirelessly with your PS3 then the latest firmware update from Sony will allow you to do exactly that (previously you could only use the feature via a wired connection).
When linked to a PS3, the PS4 controller only registers as a generic controller, so there's no touch pad functionality, rumble force and motion control. Apart from that it's still the DualShock 4 that we all know and love. However, according to some gamers on Reddit, game compatibility is a bit uneven.
We can also report that there's plenty of people who aren't able to access the feature. Out of three Gamereactor editors who've tried pairing their DualShock 4s to their PS3s, only one was successful. Other gamers have reported similar issues on various forums. so be warned, it doesn't appear to work for everybody.